This invention relates to a method for preparing an adduct of a butadiene lower polymer or butadiene lower copolymer and a .alpha.,.beta.-ethylenically unsaturated dicarboxylic acid compound.
In the field of the electrodeposition of a water paint, a butadiene lower polymer has been widely accepted as a film forming material. This fact depends upon that the coating film formed from butadiene lower polymer or copolymer has excellent film properties in view of the chemical resistance, solvent resistance, weather resistance, leveling property and so forth as compared with those prepared from the conventional film forming materials such as drying oils and alkyd resins.
In order to prepare film forming materials for water paints, it is necessary to introduce hydrophilic groups such as carboxyl, hydroxyl, ether, amino and sulfonic acid groups into the molecular structure of the material. As a method for introducing a carboxyl group as the hydrophilic group into drying oils having conjugated double bonds such as tung oil, dehydrated castor oil and isomerized drying oil, or into those having non-conjugated double bonds such as linseed oil and soybean oil, maleic anhydride is usually added to said drying oils, which are neutralized thereafter, where thus prepared modified oils are widely employed as maleic oils.
While, with regard to the introduction of the carboxyl group to the butadiene lower polymer or copolymer, it is also well known that an adduct can be prepared by heating it with a .alpha.,.beta.-ethylenically unsaturated dicarboxylic acid compound, as disclosed in Japanese Patent Publication No. 954, of 197l.
However, during the preparation of the adduct of a butadiene lower polymer or copolymer with a .alpha.,.beta.-ethylenically unsaturated dicarboxylic acid compound, the viscosity of the reaction product is largely increased as compared with that of the starting polymer, and gelatin of the product is sometimes caused. Further, when the viscosity of the adduct is excessively high, the treatment of water-solubilizing becomes very difficult.
Accordingly, several attempts have been studied and tried in order to reduce the viscosity of the adduct in the conventional process of the reaction between a .alpha.,.beta.-ethylenically unsaturated dicarboxylic acid compound and a butadiene lower polymer or copolymer. For example, use of a non-coloring stabilizer (French Patent No. 1,332,596), copper and copper compounds (Japanese patent Publications, No. 26,870 of 1968 and No. 44,557 of 1972), and alkyl amines, ammonium salts, urethane compounds and urea compounds (Japanese Patent Publications, No. 3,544 of 1973, No. 3,545 of 1973, No. 3,546 of 1973 and No. 3,547 of 1973) are well known as gelation inhibitors of the reaction materials.
Nevertheless, when non-coloring stabilizers such as hydroquinone, tert-amylhydroquinone, diphenylamine and 2,6-di-tert-butyl-4-methylphenol as disclosed in French Patent No. 1,332,596 are used, only a small addition of them causes an undesirable effect on the air drying property of some butadiene lower polymers, or at least, delays the drying, and furthermore, the effect of decreasing the viscosity of a adduct is very small or almost zero.
Further, when the copper or copper compounds as disclosed in Japanese Patent Publication Nos. 26,870 of 1968 and 44,557 of 1972 are used, a dark-colored adduct is obtained, the rate of addition reaction is low, and the viscosity of the adduct does not decrease so much.
Still further, when the alkyl amines such as diethylamine and triethylamine as disclosed in Japanese Patent Publication Nos. 3,544; 3,545; 3,546 and 3,547 of 1973 are used, the adduct is greatly colored and the addition is caused only to a small extent at a higher temperature of about 200.degree.C, while a by-product is produced owing to the reaction between maleic anhydride and said alkyl amines.